The present invention is related to sensor assemblies, and more specifically to an advantageous configuration for a pressure sensor assembly utilized to sense pressure of an ambient atmosphere and/or fluid which may be corrosive with respect to the electrical output connections utilized in the pressure sensing element. The "atmosphere" being sensed may comprise either a gas or fluid. The term "pressure transducer" is used herein to refer to the pressure sensing element itself, as opposed to the "pressure sensor" or "pressure sensor assembly" which includes the transducer and various separate discrete electrical components that process output signals provided by the transducer.
Pressure transducers comprising a silicon capacitive pressure transducer are known in which a silicon diaphragm is anodically bonded to a metallized relatively rigid glass substrate base and wherein either metallized vias or embedded pins in the base may be utilized to provide the electrical output connections of the transducer. U.S. Pat. No. 4,384,899 to Myers illustrates such a pressure transducer utilizing metallized vias, whereas copending U.S. patent application Ser. No. 696,933, filed Jan. 31, 1985 to Shak et al. illustrates a transducer element utilizing embedded pins for feedthrough electrical connections instead of metallized vias. These pressure transducers, as well as piezoresistive pressure transducers (PRT's) having wire bonds exposed to the sensing atmosphere/fluid, have been utilized in pressure sensor assemblies wherein portions of either the electrical output connections or the wire bonds, which form a part of the electrical output connections of the transducer, are directly exposed to the ambient atmosphere/fluid being sensed. The metallized via transducers and the PRT's having wire bonds are typically reflow soldered or otherwise bonded onto the top surface of a metallized carrier circuit board. Then a sealing ring is provided on the carrier about the transducer. Sometimes a silastic sealing material is provided over the transducer, but this may interfere with pressure sensing. Also, the structures discussed above do not sufficiently prevent the sensed atmosphere and/or fluid from contacting electrical output connections of the transducer.
Typically prior sensor assemblies which have transducers with discrete lead wires extending from a bottom surface, such as the above-noted Shak et al. application, either utilize a portion of the pressure transducer or an extension thereof as part of a sealing means to provide a relatively hermetic seal between the ambient pressure atmosphere/fluid being sensed and other components positioned within a pressure sensor assembly housing in which the transducer is mounted. U.S. Pat. Nos. 3,352,157 and 4,380,014 both illustrate pressure sensor assemblies in which a lateral effective extension of either the pressure sensing diaphragm or the base of the pressure transducer is utilized as a mounting shoulder for a sealing O-ring. In either occurrence, the size of the pressure transducer element is undesirably increased in order to accommodate the contemplated sealing mechanism. For mass production techniques, the pressure transducer itself should be without additional lateral extensions thereof to accommodate a sealing ring. This is especially true for the silicon and glass anodically-bonded pressure transducers discussed above.
As noted above, some of the prior sensor assemblies do not provide sufficient isolation of the electrical output connections of the transducer with respect to the sensed ambient atmosphere pressure. When the ambient atmosphere/fluid being sensed is corrosive, this can be extremely detrimental to the reliability of the pressure sensor assembly. Some pressure sensor assemblies, such as that shown in U.S. Pat. No. 4,178,921 to Simonelic et al., contemplate providing an ambient atmosphere sealing ring directly on the perimeter of the sensing diaphragm. This apparently would prevent the sensed atmosphere/fluid from contacting the transducer output connections. However, this structure also undesirably increases the size of the pressure transducer element and may compromise the electrical characteristics of the pressure transducer since the sealing ring may dampen the movement of the diaphragm in response to sensed pressure.
Therefore, prior sensor pressure assemblies have either not provided sufficient protection for the electrical output connections of the pressure transducer or they have undesirably increased the size of the pressure transducer element itself in order to accomplish the sealing which may be required when the pressure transducer is mounted in a housing.